De or het voorinvestering?

The correct Dutch article is:

de voorinvestering

Rule Words ending in -ing: almost always de. See the rule

How to use voorinvestering

the voorinvesteringde voorinvestering
this voorinvesteringdeze voorinvestering
that voorinvesteringdie voorinvestering
our voorinvesteringonze voorinvestering
your voorinvesteringjouw voorinvestering
every voorinvesteringelke voorinvestering
which voorinvestering?welke voorinvestering?
a big voorinvestering / the big voorinvesteringeen grote voorinvestering, de grote voorinvestering